On the Formation of the Double Neutron Star Binary PSR J1846-0513

The double neutron star PSR J1846-0513 is discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST)in Commensal Radio Astronomy FAST Survey.The pulsar is revealed to be harbored in an eccentric orbit with e=0.208 and an orbital period of 0.613 day.The total mass of the system is constrained to b2.6287(35)M_(⊙),with a mass upper limit of 1.3455 M_(⊙)for the pulsar and a mass lower limit of 1.2845 M_(⊙)for th companion star.To reproduce its evolution history,we perform a 1D model for the formation of PSR J1846-0513whose progenitor is assumed to be neutron star—helium(He)star system via MESA code.Since the larg eccentricity is widely believed to originate from an asymmetric supernova explosion,we also investigate th dynamical effects of the supernova explosion.Our simulated results show that the progenitor of PSR J1846-0513could be a binary system consisting of a He star of 3.3-4.0 M_(⊙)and a neutron star in a circular orbit with an initia period of~0.5 day.

Analysis of the Impact of the Blazhko Effect Both on the Van Hoof Effect and Radial Velocity Amplitude in the Star RR Lyr

The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars.In this article,we present a study of this phenomenon through the spectra of the brightest pulsating star RR Lyr of RR Lyrae stars recorded for 22 yr.We based ourselves,on the one hand,on 1268 spectra(41 nights of observation)recorded between the years 1994 and 1997 at the Observatory of Haute Provence(OHP,France)previously observed by Chadid and Gillet,and on the other hand on 1569 spectra(46nights of observation)recorded at our Oukaimeden Observatory(Morocco)between 2015 and 2016.Through this study,we have detected information on atmospheric dynamics that had not previously been detected.Indeed,the Van Hoof effect which results in a clear correlation between the radial velocities of hydrogen and those of the metallic lines has been observed and analyzed at different Blazhko phases.A correlation between the radial velocities of different metallic lines located in the lower atmosphere has been observed as well.For the first time,we were able to show that the amplitude of the radial velocity curves deduced from the lines of hydrogen and that of FeⅡ(λ4923.921?)increases toward the minimum of the Blazhko cycle and decreases toward the maximum of the same Blazhko cycle.Furthermore,we found that the Van Hoof effect is also modulated by the Blazhko effect.Thus,toward the minimum of the Blazhko cycle the Van Hoof effect is more visible and at the maximum of the Blazhko cycle,this effect is minimal.We also observed the temporal evolution of the amplitudes of the radial velocities of the lower and upper atmosphere.When observed over a long time,we can interpret it as a function of the Blazhko phases.

GRB 210323A:Signature of Long-lasting Lifetime of Supra-massive Magnetar as the Central Engine from the Merger of Binary Neutron Star

Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting~1 s.The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with E_p=1826±747.More interestingly,it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of~10^(4)s,and then follows a rapid decay with a decay slope~3.2.This temporal feature is challenging by invoking the external shock mode.In this paper,we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar,and the abrupt decay following the longlasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole.It is the short GRB(SGRB)with the longest X-ray internal plateau emission powered by a supra-massive neutron star.If this is the case,one can estimate the physical parameters of a supra-massive magnetar,and compare with other SGRBs.We also discuss the possible gravitational-wave emission,which is powered by a supra-massive magnetar and its detectability,and the possible kilonova emission,which is powered by r-process and magnetar spin-down to compare with the observed data.

Variable Stars in the 50BiN Open Cluster Survey.Ⅲ.NGC 884

Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal structure,temporal and dynamical evolutionary stages of individual stars and the host cluster.The most powerful tool for such studies is time-domain photometric observations.This paper follows the route of our previous work,concentrating on a photometric search for variable stars in NGC 884.The target cluster is the companion of NGC869,forming the well-known double cluster system that is gravitationally bound.From the observation run in 2016 November,a total of 9247 B-band CCD images and 8218Ⅴ-band CCD images were obtained.We detected a total of 15 stars with variability in visual brightness,including five Be stars,three eclipsing binaries,and seven of unknown types.Two new variable stars were discovered in this work.We also compared the variable star content of NGC 884 with its companion NGC 869.

Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

The observation of oxygen(O)-and nitrogen(N)-bearing molecules gives an idea about the complex prebiotic chemistry in the interstellar medium.Recent millimeter and submillimeter wavelength observations have shown the presence of complex O-and N-bearing molecules in the star formation regions.So,the investigation of those molecules is crucial to understanding the chemical complexity in the star-forming regions.In this article,we present the identification of the rotational emission lines of N-bearing molecules ethyl cyanide(C_(2)H_(5)CN)and cyanoacetylene(HC_(3)N),and O-bearing molecule methyl formate(CH_(3)OCHO)toward high-mass protostar IRAS18089–1732 using the Atacama Compact Array.We also detected the emission lines of both the N-and O-bearing molecule formamide(NH_(2)CHO)in the envelope of IRAS 18089–1732.We have detected the v=0 and 1 state rotational emission lines of CH_(3)OCHO.We also detected the two vibrationally excited states of HC_(3)N(v7=1 and v7=2).The estimated fractional abundances of C_(2)H_(5)CN,HC_(3)N(v7=1),HC_(3)N(v7=2),and NH_(2)CHO toward IRAS 18089–1732 are(1.40±0.5)×10^(-10),(7.5±0.7)×10^(-11),(3.1±0.4)×10^(-11),and(6.25±0.82)×10^(-11)respectively.Similarly,the estimated fractional abundances of CH_(3)OCHO(v=0)and CH_(3)OCHO(v=1)are(1.90±0.9)×10^(-9)and(8.90±0.8)×10^(-10),respectively.We also created the integrated emission maps of the detected molecules,and the observed molecules may have originated from the extended envelope of the protostar.We show that C_(2)H_(5)CNand HC_(3)N are most probably formed via the subsequential hydrogenation of the CH_(2)CHCNand the reaction between C_(2)H_(2)and CN on the grain surface of IRAS 18089–1732.We found that NH_(2)CHO is probably produced due to the reaction between NH_(2)and H_(2)CO in the gas phase.Similarly,CH_(3)OCHO is possibly created via the reaction between radical CH_(3)O and radical HCO on the grain surface of IRAS 18089–1732.

New CCD photometric investigation of the early-type overcontact binary BH Cen in the young star-forming Galactic cluster IC 2944

BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A3 = 0.024 d and a period of P3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M2 = 2.8×10^-6 M⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.

NSVS 2569022:a peculiar binary among W UMa stars with extremely small mass ratios

Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total eclipse of W subtype and the mass ratio is well-determined. Its extremely small value of only 0.077 implies that the target will probably experience instability and a possible merger. This value ranks NSVS 2569022 in sixth place among binaries with the smallest mass ratio. Based on an empirical relation of ＂period - total mass＂ for low mass-ratio binaries, we estimate the global parameters of NSVS 2569022： masses M1 = 1.17 M⊙ and M2 = 0.09 M⊙; radii R1 = 1.19 R⊙ and R2 = 0.38 R⊙; luminosities L1 = 1.73 L⊙ and L2 = 0.17L⊙. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out to be a peculiar binary among W UMa stars with extremely small mass ratios due to its unexpectedly small fill-out factor of only 0.014 （slightly overcontact configuration）.

Supernova neutrinos in a strangeon star model

The neutrino burst detected during supernova SN 1987A is explained in a strangeon star model, in which it is proposed that a pulsar-like compact object is composed of strangeons （strangeon： an abbreviation for ＂strange nucleon＂）. A nascent strangeon star＇s initial internal energy is calculated, with the inclusion of pion excitation （energy around 1053 erg, comparable to the gravitational binding energy of a collapsed core）. A liquid-solid phase transition at temperature - 1 - 2 MeV may occur only a few tens of seconds after core collapse, and the thermal evolution of a strangeon star is then modeled. It is found that the neutrino burst observed from SN 1987A can be reproduced in such a cooling model.

The Guest Star of AD185 must have been a Supernova

The ＂guest star＂ of AD185, recorded in the ancient Chinese history the Houhanshu, has been widely regarded as a supernova. However, some authors have suggested that the guest star might have been a comet. It has also been proposed that the record is the concatenation of a nova with a comet made by an early compiler. We have checked the record of the guest star, comparing it with records of comets in the same history. We find that most descriptions of comets clearly indicate motion, whereas the record of the guest star does not. We further argue that the term ＂yan＂ used to describe the star＇s ＂size＂ might be short for yanchuang （seat bed）, and ＂half a yan＂ would be simply as an imaginary figuration of the ancient observer. Moreover, we show that the term ＂hou -year＂ （hou-nian） most probably means the year after next. We argue that the asterism Southern Gate consisted of the stars α andβ Cen. We conclude that the record describing the guest star of AD 185 is completely different from any comet record in the same history, and that it almost certainly was a supernova.

Aquila Rift区域年轻星候选体的搜寻

使用德国Th(u|¨)ringer Landessternwarte Tautenburg(TLS)的2 m望远镜对Aquila Rift的16个区域进行了Hα、R和I共3个波段的成像观测.这些观测区域大约覆盖了Aquila Rift 7平方度的天区.除去3个数据质量不高的天区,对其余的13个区域进行了测光分析,从中证认出点源,并利用双色图的方法最终证认出7颗Hα发射线星候选体.这7个候选体是从5个观测区域中选出的,其中3颗位于银道面区域,4颗位于银纬高于4°的区域.对于这5个天区,证认了其中点源的2MASS对应体,并利用双色图的方法进一步分析了7个Hα发射线星候选体的性质.这些Hα发射线星候选体的近红外辐射并没有明显的红外超现象,有一颗还落在了主序分支上.这也说明有Hα发射的年轻星并不都伴随有红外超现象.Hα发射线观测和红外超观测的结果是相互补充的.如果将这7颗Hα发射线星候选体作为年轻星候选体,则Aquila Rift区域的年轻星数目是较少的.对于这些候选体的进一步证认还需要后续的光谱观测.

Variable stars in the 50BiN open cluster survey.Ⅱ.NGC 869

This work presents a time-series photometric variability survey of the young open cluster NGC 869.More than 13000 CCD frames in the BV filters were collected on 19 nights between 2014 November 6 and 2014 December 24.In a 20’×20’field centered on the cluster,we detected a total of 28 stars showing photometric variability,12 of which are new discoveries.The classifications and memberships of the variable stars are discussed according to the behaviors and periods of the light curves as well as their positions on the H-R diagram.These results conclude that 22 variable stars are probable members of the cluster while six other stars belong to the field star population.They are categorized as 18 pulsating variable stars(fourβCep,seven SPB,oneβCep/SPB,four Be stars,and twoδSct/γDor candidates),seven eclipsing binaries(five EA and two EB)and three unknown type stars.

OO Aquilae:a solar-type contact binary with intrinsic light curve changes

New multi-color photometry of the solar-type contact binary OO Aql was obtained in 2012 and2013, using the 60 cm telescope at Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences. From two sets of light curves LC_1 and LC_2, photometric models were performed by using the 2003 version of the Wilson-Devinney code. The overcontact factor of the binary system was determined to be f = 37.0（±0.5）%. The intrinsic variability of this binary occurs in light maxima and minima, which could result from a possible third component and magnetic activity of the late type components. Based on all available light minimum times, the orbital period may change in a complicated mode,i.e., sudden period jumps or continuous period variations. The period of OO Aql may possibly undergo a secular period decrease with a rate of d P /dt =-3.63（±0.30） × 10^（-8）d yr^（-1）, superimposed by two possible cyclic variations in the O- C curve. The long-term period decrease may be interpreted as conserved mass transfer from the more massive component to the less massive one. The 21.5-yr oscillation may be attributed to cyclic magnetic activity, and the 69.3-yr one may result from the light-time effect of an unseen tertiary body.

Resonant cyclotron scattering in pulsar magnetospheres and its application to isolated neutron stars

Resonant cyclotron scattering （RCS） in pulsar magnetospheres is considered. The photon diffusion equation （Kompaneets equation） for RCS is derived. The photon system is modeled three dimensionally. Numerical calculations show that there exist not only up scattering but also down scattering of RCS, depending on the parameter space. RCS＇s possible applications to spectral energy distributions of magnetar candidates and radio quiet isolated neutron stars （INSs） are pointed out. The optical/UV excess of INSs may be caused by the down scattering of RCS. The calculations for RX J1856.5-3754 and RX J0720.4-3125 are presented and compared with their observational data. In our model, the INSs are proposed to be normal neutron stars, although the quark star hypothesis is still possible. The low pulsation amplitude of INSs is a natural consequence in the RCS model.

Time-resolved CCD photometry and time-series analysis of the RR Lyrae type star RR Gem

We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean magnitudes, 11.277(V) and 11.063(I) mag respectively. We confirm its variability type as RRab/BL because it manifests the Blazhko effect, and it also exhibits asymmetric light curves(steep ascending branches), periods from 0.3 to 1.0 d and amplitudes from 0.3 to 2 mag in V. They are fundamental mode pulsators.

Study of the puzzling abundance pattern of the neutron-capture elements in LMC star J053253.51–695915.1

Object J053253.51–695915.1(J053253)in the Large Magellanic Cloud(LMC)is reported as a young stellar object(YSO).Its chemical abundances reflect the initial composition of the gas cloud in which the star formed.However,the discovery that this star shows the enhancement of the neutron(n)-capture elements and the higher ratio of the heavier n-capture elements relative to the lighter n-capture elements is puzzling.Using an abundance decomposed method,we explore the astrophysical origins of the n-capture elements in this star.We find that the abundance characteristic of the higher ratio of the heavier n-capture elements to the lighter n-capture elements can be explained by the pollution of the r-process event and the contamination of the s-process material.

BV(RI )c photometric study of three variable PMS stars in the field of V733 Cephei

This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars are located in the field of the PMS star V733 Cep within the Cepheus OB3 association. All stars from our study show rapid photometric variability in all-optical passbands. In this paper, we describe and discuss the photometric behavior of these stars and the possible reasons for their variability. In the light variation of two of the stars, we found periodicity.

Searching for Variable Stars in the Field of NGC 7789

We present the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 7789. In a field of about one degree centering on the cluster, a total of 28 new variable stars are discovered (14 W UMa systems, nine EA-type eclipsing binaries, one RR Lyr star, and four unclassified). In addition, we recovered 11 old variables previously discovered by other authors. Preliminary parameters are given for some of these variables.

Pulsations of the High-Amplitude δ Scuti star YZ Bootis

We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory（XAO）and the Xinglong 85-cm telescope of National Astronomical Observatories,Chinese Academy of Sciences（NAOC）.Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics,with the fourth and fifth being newly detected.Thirtynine new times of maximum light are determined from the light curves,and combined with those in the literature,we construct the O-C diagram,derive a new ephemeris and determine a new value for the updated period of 0.104091579（2）.In addition,the O-C diagram reveals an increasing rate of period change for YZ Boo.Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo.The mass and age of YZ Boo are hence derived as M=1.61±0.05 M_⊙ and age=（1.44±0.14）×10~9 yr,respectively.With both the frequency of the fundamental radial mode and the rate of period change,YZ Boo is located at the post main sequence stage.

Gas infall in the massive star formation core G192.16–3.84

Previous observations have revealed an accretion disk and outflow motion in the high-mass starforming region G192.16–3.84, but collapse has not been reported before. Here we present molecular line and continuum observations toward the massive core G192.16–3.84 with the Submillimeter Array. C18 O(2–1) and HCO+(3–2) lines show pronounced blue profiles, indicating gas infalling in this region. This is the first time that infall motion has been reported in the G192.16–3.84 core. Two-layer model fitting gives infall velocities of 2.0±0.2 and 2.8±0.1 km s-1. Assuming that the cloud core follows a power-law density profile(ρ∝ r1.5), the corresponding mass infall rates are(4.7±1.7)×10-3 and(6.6±2.1)×10-3 M⊙yr-1 for C18 O(2–1) and HCO+(3–2), respectively. The derived infall rates are in agreement with the turbulent core model and those in other high-mass star-forming regions, suggesting that high accretion rate is a general requirement for forming a massive star.

Optical flare events on the RS Canum Venaticorum star UX Arietis

Based on long-term high-resolution spectroscopic observations obtained during five observing runs from 2001 to 2004, we study optical flare events and chromospheric activity variability of the very active RS CVn star UX Ari. By means of the spectral subtraction technique, several optical chromospheric activity indicators （including the He IDa, Na I D1, D2 doublet, Ha and Ca II IRT lines） covered in our echelle spectra were analyzed. Four large optical flare events were detected on UX Ari during our observations, which show prominent He I D3 line emission together with great enhancement in emission of the Ha and Ca II IRT lines and strong filled-in or emission reversal features in the Na ! D1, D2 doublet lines. The newly detected flares are much more energetic than previous discoveries, especially for the flare identified during the 2002 December observing run. Optical flare events on UX Ari are more likely to be observed around two quadratures of the system, except for our optical flares detected during the 2004 November observing run. Moreover, we have found rotational modulation of chromospheric activity in the Ha and Ca II IRT lines, which suggests the presence of chromospherically active longitudes over the surface of UX Ari. The change in chromospherically active longitudes among our observing runs, as well as the variation in chromospheric activity level from 2001 to 2004, indicates a long-term evolution of active regions.